Conventionally, a known presser foot device for a sewing machine has a mechanism in which, during a sewing operation, a presser foot is vertically moved with a small stroke in a predetermined range, and, in other operations such as a thread cutting operation and a frame movement, the presser foot is retracted as required to a position which is higher in level than the vertical movement range.
For example, Japanese patent publication (Kokai) No. 07231 991 A discloses a device in which a presser foot is attached via plural links to the tip end of a driving arm that is swung by the rotation of an eccentric cam, and the presser foot is vertically moved in synchronization with the rotation of the main shaft. When the presser foot is to be retracted, a retraction lever is rotated so that the driving arm is rotated in a direction along which the driving arm is separated from the eccentric cam. Although not shown in the figure, the publication discloses a structure in which a spring for causing a cam follower unit of the driving arm to abut against the eccentric cam is disposed.
Japanese patent publication (Kokai) No. 06238078 A discloses a device in which a cam groove for vertically moving a presser foot is formed in the outer peripheral face of a driving cam, a cam follower is fitted into the driving cam, and, during a sewing operation, the driving cam is rotated in synchronization with the main shaft, thereby vertically moving the presser foot with a predetermined stroke. A mechanism for upward retracting the presser foot is configured so that a retraction groove is formed in a part of the wall opposite to the cam face of the cam groove and, as required, the cam follower is retracted into the retraction groove, whereby the presser foot is moved through a link so as to be elevated to a retraction position. In the device, an urging force for abutting the cam follower against the cam face is produced by a second compression spring.
In such prior art techniques, when the presser foot is to be upward retracted, the cam follower must be moved against the urging force exerted by the spring which causes the cam follower to abut against the cam face. In order to move the cam follower with correctly following the cam face, the spring has a relatively large urging force. Therefore, a prior art device has a problem in that a large load is applied to a presser foot retraction mechanism. In an embroidery sewing machine, particularly, the number of heads is increasing. In such a multi-head sewing machine, therefore, the total of loads which are respectively applied to heads has a large value, with the result that, during a period when the main shaft of the multi-head sewing machine is rotated, a considerably large load is applied as a whole to the presser foot retraction mechanism. This load produces a large burden on the main shaft.
In the device disclosed in Japanese patent publication (Kokai) No. 06238078 A, when the presser foot which has been once retracted to a raised position is to be returned to an operating position, the main shaft cannot be driven until the cam follower is returned from the retraction groove into the cam groove. The device disclosed in Japanese patent publication (Kokai) No. 07231991 A has the structure in which the presser foot is retracted obliquely rearward. In the device also, therefore, the main shaft cannot be driven until the presser foot is returned to an operating position so that a through hole of the presser foot is positioned immediately below a stitching needle.
Consequently, such devices of the prior art have another problem in that a long period is required for the sewing operation to be restarted after a presser foot is retracted.